FUNCTION: [Summary is not available for the mouse gene. This summary is for the human ortholog.] The protein encoded by this gene is predicted to have a single transmembrane (TM)-spanning domain and multiple copies of an immunoglobulin-like plexin-transcription-factor domain. Alternative splicing results in two transcript variants encoding different isoforms. Other alternatively spliced transcripts have been described, but the full length sequences have not been determined. Several of these transcripts are predicted to encode truncated products which lack the TM and may be secreted. Mutations in this gene cause autosomal recessive polycystic kidney disease, also known as polycystic kidney and hepatic disease-1. [provided by RefSeq, Jul 2008] PHENOTYPE: Mice homozygous for a mutation in this gene display variable progressive liver cysts and fibrosis, but do not display kidney cysts and are fertile. Mice homozygous for a hypomorphic and null allele display renal, pancreatic, billiary and liver cysts. [provided by MGI curators]